Polarizing plate, optical element, and liquid crystal display

Abstract

A polyvinyl alcohol-based polarizing film is provided, and the polarizing film has excellent surface smoothness while the light transmittance and the polarization degree are improved due to the high stretch ratio. The polarizing film is obtained from a polyvinyl alcohol film having a thickness ranging from 85 μm to 150 μm by dyeing the film with a dichroic substance and stretching it to 4-7 times its original length. The polarizing film has a light transmittance ranging from 35% to 50% and a polarization degree of at least 80%, and the surface roughness in a direction perpendicular to the stretching axis is at most 0.04 μm based on a centerline average roughness. A transparent protective layer or a transparent protective plate comprising the transparent protective layer is formed on at least one surface of the polarizing film in order to provide a polarizing plate. The transparent protective layer can be subject to a pre-treatment selected from a hard-coat treatment and an anti-glare treatment. Additional optical layers are laminated on the polarizing plate in order to provide an optical element. A polarizing plate or an optical element comprising the above-mentioned polarizing film has an excellent light transmittance and polarization degree, so that stripe-shaped streaks inhibiting visibility will not be observed substantially even in a reflection mode.

1. A polarizing plate comprising a polarizing film,
 wherein the polarizing film is composed of a polyvinyl alcohol film having a thickness ranging from 85 μm to 150 μm, dyed with a dichroic substance and stretched to 4-7 times,  
 the polarizing film has a light transmittance ranging from 35% to 50% and a polarization degree of at least 80%; a surface roughness in a direction perpendicular to the stretching axis of at most 0.04 μm based on a centerline average roughness; and  
 the polarizing plate further comprises a transparent protective layer disposed on at least one surface of the polarizing film.  
 
     
     
       2. The polarizing plate according to  claim 1 , wherein the transparent protective layer is subject to a pre-treatment selected from the group consisting of a hard-coat treatment and an anti-glare treatment. 
     
     
       3. The polarizing plate according to  claim 1 , wherein the polyvinyl alcohol film has a thickness ranging from 90 μm to 130 μm. 
     
     
       4. The polarizing plate according to  claim 1 , wherein the polyvinyl alcohol film is stretched to 5.5-6.5 times. 
     
     
       5. The polarizing plate according to  claim 1 , wherein the polarizing film has a light transmittance ranging from 40% to 50% and a polarizing degree of at least 90%, and the surface roughness in a direction perpendicular to a stretching axis is at most 0.03 μm based on the centerline average roughness. 
     
     
       6. The polarizing plate according to  claim 1 , wherein the polarizing film has a light transmittance ranging from 42% to 50% and a polarizing degree of at least 95%, and the surface roughness in a direction perpendicular to a stretching axis is at most 0.02 μm based on the centerline average roughness. 
     
     
       7. The polarizing plate according to  claim 1 , wherein the transparent protective layer comprises at least one material selected from the group consisting of a cellulose-based resin, a polycarbonate-based resin, and a polyester-based resin. 
     
     
       8. The polarizing plate according to  claim 7 , wherein the transparent protective layer has a thickness ranging from 1 μm to 300 μm. 
     
     
       9. The polarizing plate according to  claim 1 , further comprising a reflective layer or a semitransparent reflective layer. 
     
     
       10. An optical element comprising a laminate of a polarizing plate and at least one optical layer selected from the group consisting of a retardation plate, a viewing angle compensating film, a photoconcentrating plate, a brightness enhancement plate and a light diffusion plate,
 wherein the polarizing plate comprises a polarizing film,  
 the polarizing film comprises a polyvinyl alcohol film having a thickness ranging from 85 μm to 150 μm, dyed with a dichroic substance and stretched to 4-7 times,  
 the polarizing film has a light transmittance ranging from 35% to 50% and a polarization degree of at least 80%; a surface roughness in a direction perpendicular to the stretching axis of at most 0.04 μm based on a centerline average roughness, and  
 the polarizing plate further comprises a transparent protective layer disposed on at least one surface of the polarizing film.  
 
     
     
       11. The optical element according to  claim 10 , wherein the transparent protective layer is subject to a pre-treatment selected from the group of a hard-coat treatment and an anti-glare treatment. 
     
     
       12. The optical element according to  claim 10 , wherein the optical layer comprises at least one material selected from the group consisting of a retardation plate and a brightness enhanced plate. 
     
     
       13. The optical element according to  claim 12 , wherein the retardation plate comprises at least one material selected from the group consisting of a bireflingent film comprising a plastic stretched film, an oriented film of either a discotic or nematic liquid crystal polymer, and a sheet comprising a film substrate and an oriented liquid crystal layer of a discotic or nematic liquid crystal supported by the film substrate. 
     
     
       14. The optical element according to  claim 12 , wherein the brightness-enhanced plate comprises at least one material selected from the group consisting of a laminate of thin films distinguished from each other in the refractive index anisotropy, an oriented film of a cholesteric liquid crystal polymer, and a sheet comprising a film substrate and an oriented liquid crystal layer of a cholesteric liquid crystal polymer supported by the film substrate. 
     
     
       15. The optical element according to  claim 10 , wherein the polarizing plate and the optical layer are adhered integrally with each other through a pressure-sensitive adhesive layer. 
     
     
       16. The optical element according to  claim 10 , wherein the polyvinyl alcohol film has a thickness ranging from 90 μm to 130 μm. 
     
     
       17. The optical element according to  claim 10 , wherein the polyvinyl alcohol film is stretched to 5.5-6.5 times. 
     
     
       18. The optical element according to  claim 10 , wherein the polarizing film has a light transmittance ranging from 40% to 50% and a polarizing degree of at least 90%, and the surface roughness in a direction perpendicular to a stretching axis is at most 0.03 μm based on the centerline average roughness. 
     
     
       19. The optical element according to  claim 10 , wherein the polarizing film has a light transmittance ranging from 42% to 50% and a polarizing degree of at least 95%, and the surface roughness in a direction perpendicular to a stretching axis is at most 0.02 μm based on the centerline average roughness. 
     
     
       20. The optical element according to  claim 10 , wherein the transparent protective layer comprises at least one material selected from the group consisting of a cellulose-based resin, a polycarbonate-based resin, and a polyester-based resin. 
     
     
       21. The optical element according to  claim 20 , wherein the transparent protective layer has a thickness ranging from 1 μm to 300 μm. 
     
     
       22. A liquid crystal display comprising a liquid crystal cell and an optical element disposed on at least one surface of the liquid crystal cell,
 wherein the optical element comprises a laminate of a polarizing plate and at least one optical layer selected from the group consisting of a retardation plate, a viewing angle compensating film, a photoconcentrating plate, a brightness enhancement plate and a light diffusion plate,  
 wherein the polarizing plate comprises a polarizing film,  
 the polarizing film comprises a polyvinyl alcohol film having a thickness ranging from 85 μm to 150 μm, dyed with a dichroic substance and stretched to 4-7 times,  
 the polarizing film has a light transmittance ranging from 35% to 50% and a polarization degree of at least 80%; a surface roughness in a direction perpendicular to the stretching axis of at most 0.04 μm based on a centerline average roughness, and  
 the polarizing plate further comprises a transparent protective layer disposed on at least one surface of the polarizing film.  
 
     
     
       23. The optical element according to  claim 10 , wherein the polarizing film is composed of the polyvinyl alcohol film. 
     
     
       24. The liquid crystal display according to  claim 22 , wherein the polarizing film iscomposed of the polyvinyl alcohol film.